The development and advantages of beryllium capsules for the National Ignition Facility

Abstract

Capsules with beryllium ablators have long been considered as alternatives to plastic for the National Ignition Facility laser ; now the superior performance of beryllium is becoming well substantiated . Beryllium capsules have the advantages of relative insensitivity to instability growth, low opacity, high tensile strength, and high thermal Zimmerman and W. L. h e r , Comments Plasmas Phys. Controlled Thermonucl. Fusion, 2 , 5 1 (2975)l results that particular beryllium capsule designs are several times less sensitive than the CH point design to instability growth from DT ice roughness. These capsule designs contain more ablator mass and leave some beryllium unablated at ignition. By adjusting the level of copper dopant, the unablated mass can increase or decrease, with a corresponding decrease or increase in sensitivity to perturbations . A plastic capsule with the same ablator mass as the beryllium and leaving the same unablated mass also shows this reduced perturbation sensitivity. Beryllium's low opacity permits the creation of 250 eV capsule designs. Its high tensile strength allows it to contain DT fuel at room temperature. Its high thermal conductivity simplifies cryogenic fielding.

X-ray imaging of cryogenic deuterium-tritium layers in a beryllium shell

“…This design can tolerate roughner D-T surfaces, compared to plastic ablators which require less than 1 µm RMS D-T surfaces to ignite. [1,2] Characterization of the solid D-T surface roughness is requried to compare ignition experiments with simulations. However, only limited characterization of the solid D-T fuel layer inside of the Be(Cu) shell has been possible.…”

Plastic ablator ignition capsule design for the National Ignition Facility

“…In an effort to improve capsule performance, beryllium doped with copper was proposed as an ablator and shown, in simulations, to be markedly more stable hydrodynamically than plastic [5,6]. Nearly concurrently, graded doped designs were introduced for both copperdoped beryllium [7] and later germanium-doped plastic.…”

Increasing robustness of indirect drive capsule designs against short wavelength hydrodynamic instabilities

“…At that time it was believed that fabrication and fielding would be easiest with uniformly doped CH(Br). Targets were subsequently proposed with ablators of uniformly Cu doped Be [5], and of undoped polyimide [6]. Be is doped with Cu since it is known that Cu dissolves atomically in solid Be at the relevant concentrations of ~1%; the choice of dopant material is not tightly constrained by the implosion physics, provided that the dopant increases the opacity to hard x-rays while minimally increasing the opacity for the bulk of the x-rays in the drive.…”